Abstract:Auxin and cytokinin direct cell proliferation and differentiation during the in vitro culture of plant cells, but the molecular basis of these processes, especially de novo shoot regeneration, has not been fully elucidated. Here, we describe the regulatory control of shoot regeneration in Arabidopsis thaliana (L.) Heynh, based on the interaction of ARABIDOPSIS RESPONSE REGULATOR12 (ARR12) and WUSCHEL (WUS). The major site of ARR12 expression coincided with the location where the shoot apical meristem (SAM) ini… Show more
“…This implies the existence of a developmental-and tissue-specific context necessary for both cytokinin-mediated WUS activation and WUS-dependent induction of a change in organ identity. Recently, the type-B ARRs ARR1, ARR2, ARR10 and ARR12 have been implicated in directly interacting with WUS promoter (Dai et al, 2017;Meng et al, 2017;Wang et al, 2017;Zhang et al, 2017;Zubo et al, 2017). However, similar to our study, showing a much larger TCSn:GFP domain when compared with highly focused WUS activity (Fig.…”
Section: Respecification Of Organ Primordia Identity Is Associated Wisupporting
Mutual interactions of the phytohormones, cytokinins and auxin determine root or shoot identity during postembryonic organogenesis in plants. However, our understanding of the role of hormonal metabolism and perception during early stages of cell fate reprogramming is still elusive. Here we show that auxin activates root formation, whereas cytokinins mediate early loss of the root identity, primordia disorganisation and initiation of shoot development. Exogenous and endogenous cytokinins influence the initiation of newly formed organs, as well as the pace of organ development. The process of shoot apical meristem establishment is accompanied by accumulation of endogenous cytokinins, differential regulation of genes for individual cytokinin receptors, strong activation of AHK4-mediated signalling and induction of the shoot-specific homeodomain regulator The last is associated with upregulation of isopentenyladenine-type cytokinins, revealing higher shoot-forming potential when compared with-zeatin. Moreover, AHK4-controlled cytokinin signalling negatively regulates the root stem cell organiser in the root quiescent centre. We propose an important role for endogenous cytokinin biosynthesis and AHK4-mediated cytokinin signalling in the control of-induced organ identity.
“…This implies the existence of a developmental-and tissue-specific context necessary for both cytokinin-mediated WUS activation and WUS-dependent induction of a change in organ identity. Recently, the type-B ARRs ARR1, ARR2, ARR10 and ARR12 have been implicated in directly interacting with WUS promoter (Dai et al, 2017;Meng et al, 2017;Wang et al, 2017;Zhang et al, 2017;Zubo et al, 2017). However, similar to our study, showing a much larger TCSn:GFP domain when compared with highly focused WUS activity (Fig.…”
Section: Respecification Of Organ Primordia Identity Is Associated Wisupporting
Mutual interactions of the phytohormones, cytokinins and auxin determine root or shoot identity during postembryonic organogenesis in plants. However, our understanding of the role of hormonal metabolism and perception during early stages of cell fate reprogramming is still elusive. Here we show that auxin activates root formation, whereas cytokinins mediate early loss of the root identity, primordia disorganisation and initiation of shoot development. Exogenous and endogenous cytokinins influence the initiation of newly formed organs, as well as the pace of organ development. The process of shoot apical meristem establishment is accompanied by accumulation of endogenous cytokinins, differential regulation of genes for individual cytokinin receptors, strong activation of AHK4-mediated signalling and induction of the shoot-specific homeodomain regulator The last is associated with upregulation of isopentenyladenine-type cytokinins, revealing higher shoot-forming potential when compared with-zeatin. Moreover, AHK4-controlled cytokinin signalling negatively regulates the root stem cell organiser in the root quiescent centre. We propose an important role for endogenous cytokinin biosynthesis and AHK4-mediated cytokinin signalling in the control of-induced organ identity.
Cytokinin fulfills its diverse roles in planta through a series of transcriptional responses. We identify the in vivo DNA binding site profiles for three genetically redundant type-B ARABIDOPSIS RESPONSE REGULATORS (B-ARRs): ARR1, ARR10, and ARR12. The expression and genome-wide DNA binding locations of the three B-ARRs extensively overlap. Constructing a primary cytokinin response transcriptional network reveals a recurring theme of widespread cross-regulation between the components of the cytokinin pathway and other plant hormone pathways. The B-ARRs are found to have similar DNA binding motifs, though sequences flanking the core motif were degenerate. Cytokinin treatments amalgamate the three different B-ARRs motifs to identical DNA binding signatures (AGATHY, H(a/t/c), Y(t/c)) which suggests cytokinin may regulate binding activity of B-ARR family members. Furthermore, we find that WUSCHEL, a key gene required for apical meristem maintenance, is a cytokinin-dependent B-ARR target gene, demonstrating the importance of the cytokinin transcription factor network in shoot development.
“…WUS transcription is activated by a complex of factors including B-type ARABIDOPSIS RESPONSE REGULATOR (ARR) and HDIII-ZIP family proteins ( Supplementary Table 1 and Figure 1 ). In separate experiments, overexpression of ARR2 and ARR12 led to roughly twofold increases in number of shoots from callus in vitro ( Dai et al, 2017 ; Zhang et al, 2017 ). Contrary to the roles of B-type ARR genes, overexpression of the A-type led to strong suppression of in vitro organogenic capacity ( Osakabe et al, 2002 ; Buechel et al, 2010 ).…”
Section: Developmental Genes As Tools For Transformation Improvementmentioning
The incorporation of DNA into plant genomes followed by regeneration of non-chimeric stable plants (transformation) remains a major challenge for most plant species. Forest trees are particularly difficult as a result of their biochemistry, aging, desire for clonal fidelity, delayed reproduction, and high diversity. We review two complementary approaches to transformation that appear to hold promise for forest trees.
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